I. Field of the Invention
This invention relates generally to ECG apparatus for recording and displaying ECG signals developed on a plurality of body contacting surface electrodes, and more particularly to an apparatus and method for enhancing the detection and recording of atrial depolarization events (P-waves) by selectively inserting appropriately signal processed ECG data into the ECG input data stream during a time interval in which P-wave activity is expected to occur.
II. Discussion of the Prior Art
Clinicians typically use a surface ECG to verify cardiac tissue cardiac tissue capture from an implanted pacemaker pulse. Because of the inherent low amplitude of atrial activity, P-waves are often difficult to observe on a surface ECG, especially in patients having diseased or damaged hearts. This has traditionally created a challenge for clinicians when assessing atrial capture by a pacemaker. Thus, a need exists for an ECG apparatus and a method of operating same in such a way that the detection of P-waves is enhanced. The present invention meets that need by providing real-time algorithms for enhancing the visibility of P-waves so that atrial capture by pacing pulses from an implanted cardiac rhythm management device (CRMD) can be assessed.
Conventional ECG systems filter data picked up by skin-contacting electrodes positioned at predetermined locations on a patient""s body to a bandwidth of around 100 to 150 Hz. While the ventricular depolarization (R-wave) often contains frequencies up to 100 Hz, P-waves contain a lower spectral energy. By filtering the data stream to a bandwidth of 30 Hz or less, the signal-to-noise ratio can be increased when observing P-waves. Taking this into account, the algorithm of the present invention applies the ECG input signal train from a pair of skin-contacting electrodes to first and second signal processing channels where the first channel includes a low pass filter having a cut-off frequency capable of attenuating spectral energies characteristic of ventricular depolarization while passing spectral energies characteristic of atrial depolarization. The second channel comprises a signal delay configured to match the signal delay inherent in the low pass filter. The ECG input signal train is made to normally flow through the second channel, but upon detection of an atrial stimulating pulse produced by the implanted CRMD, the ECG input signal train is made to flow through the first channel for a predetermined time. By providing separate signal processing channels where the first channel includes a low pass filter having a cut-off frequency of about 30 Hz and the second channel includes an all pass filter that subjects the input ECG signal train to a delay corresponding to that of the low-pass filter, the 30 Hz data can be inserted in place of the 100 Hz data stream for a predetermined time interval, e.g., 150 to 200 milliseconds, following a detection of an atrial passing pulse. The 150 to 200 millisecond interval is sufficiently long that a P-wave should have been evoked if the amplitude of the atrial passing pulse results in capture.
The present invention also teaches a way in which the optimally filtered signal for observing P-waves can be seamlessly inserted into the 100 Hz data stream using a digital signal processing algorithm involving a weighted averaging technique.